Asking our existing SaaS customers for references of potential customers

Add a referral tool into your app (when they login they get a modal / note), or send an email with a referral widget (make it as easy as possible for them to do it). Each referral should add some value to the user's existing plan like adding extra storage / units or reducing cost. This has actually been the most successful growth strategy for many startups like dropbox who offered extra storage space for referrals.